Recently, transponders, which have a transmitting and receiving functions and a storing function, are provided to pneumatic tires. By using the transponders, tire manufactures control the manufacturing of tires, and tire purchasers control tire service histories, and obtain information on inflation pressures, temperature, and the like of tires. As ways of providing such transponders, for example, there are methods in which a transponder is embedded in a tire structure, and in which a transponder is adhered to the internal surface of a tire (for example, refer to Patent Document 1 and Patent Document 2).
However, a portion of the transponder embedded in the tire structure or of the transponder adhered to the internal surface of the tire cannot be identified at all when viewed from the outside. For this reason, the portion needs to be searched for using a read device. In a case of a common transponder, e.g., particularly one for individual recognition, since a read distance (a communication range) when data are read is not greater than 1 meter, a position where the transponder responds needs to be searched while moving a read device along the circumferential direction of the tire.
As a result, in a case where, for example, a tire is mounted on a vehicle so that a transponder is located on a side of the tire, the side facing laterally inward toward the vehicle, it is difficult to transmit an electric wave of the read device to the transponder, and is difficult to search the transponder. Particularly, in a case where the vehicle stops in a way that the transponder is located closed to the ground surface, it is necessary to move the vehicle, and again perform the reading operation. For a passive transponder which functions with transmitted energy from the outside, the read device needs to be maintained close to the passive transponder at the time of communication. However, unless the position of the transponder is accurately determined, energy transmission is less efficient, and an unnecessarily long period of time is needed for performing a communication operation with the transponder.    Patent Document 1: Japanese Utility Model Kokai Application No. Hei 2-123404    Patent Document 2: Japanese Patent Kokai Application No. Hei 7-132713